Solar thermal energy is a technology for harnessing solar energy in the form of heat. The thermal energy of solar radiation is absorbed by an absorber body in a solar thermal collector in which a working fluid is heated by the absorber body and circulated between the solar thermal collector and the end use. Traditional solar thermal systems are specifically used in either power plant electricity generation, hot water heating, or space heating and cooling. However, due to the current designs of available solar thermal technology, a solar thermal system that concurrently provides all of the above services to a residential or commercial building (essentially a “net-zero building”) does not exist.
The primary limitation with existing solar thermal systems is a conflict between two properties. The first property being that solar thermal systems are most efficient when its solar collectors operate at ambient temperature, that is, the hotter a solar collector gets above ambient, the more heat energy it loses to the environment via conduction, convection, and radiation. This directly opposes with the second property being that the working fluid inside the solar thermal collector must be at a greater temperature than that of the end use for heat to move in the desired direction. As a result, a contradiction occurs being that having a high solar collector temperature is required for collecting more usable heat energy, yet a higher solar collector temperature also means losing more heat energy. Therefore, existing solar thermal systems are extremely inefficient at high temperature differentials, meaning that they are unable to provide a building with enough energy to completely satisfy its needs.